Since the end of the Cold War, the United Nations Security Council has become the preeminent international actor in the resolution of armed conflicts. This is especially true of non-international armed conflicts (or NIACs), now far more common than inter-state armed conflicts (IACs). The Council has developed a substantial track record of quelling hostilities in NIACs, negotiating peace agreements, supervising transitions from war to peace and designing new political and legal institutions for post-conflict societies.

But while the Council’s omnipresence in NIACs is now unremarkable, the legal consequences of its actions have hardly been examined. Few, if any scholars have asked whether obligations the Council has imposed on NIAC parties should contribute to norms of customary international law regulating various aspects of those conflicts. Omitting Council practice makes little sense, given that states have repeatedly turned to the Council as their chosen agent to address NIACs. A continued focus on state action alone could result (and arguably already has resulted) in a body of customary norms that is increasingly disconnected from how the international community actually addresses NIACs.

This article is the first attempt to fill this gap. Our analysis is based on a newly-compiled dataset of all Council resolutions passed on the most consequential NIACs from 1990 to 2013. We coded 1057 Security Council resolutions during that period, representing 56 NIACs. We found the Council has regularly obligated NIAC parties to act in ways that diverge from otherwise-application international law in at least four significant areas.

For example, are peace agreements ending NIACs considered legally binding? Debate involving traditional sources of custom has been indeterminate, but the Council has been clear in its view that such agreements must be followed. Are non-state rebel groups are bound by human rights obligations? Scholars are divided but the Council has been consistent and unequivocal in applying human rights standards to such groups. Should elections be held in the immediate aftermath of peace settlements in NIACs? Some scholars argue there is no more important time to adhere to international standards of democratic politics. Others argue that immediate post-conflict elections are frequently destabilizing and may actually end up undermining democratic transitions. The Council has consistently sided with the former view.

We argue that in imposing these obligations the Council has acted as an agent for other UN member states. In attributing Council-imposed obligations to the entire UN membership, we extend the Council’s preeminent role in the collective security regime to the realm of generating practice constitutive of customary international law. The patterns of obligation found in Council resolutions on NIACs should serve as important evidence of customary international law. Failure to account for the Council’s centrality in resolving NIACs – substantially exceeding national interventions in scope and frequency – would consign this critical international practice to a legal black hole.